A conventionally known electrostatic actuator includes a stator that is provided with electrodes and a movable element that is disposed on the stator and has a resin substrate and a resistive film provided on the resin substrate.
In such an electrostatic actuator, the stator and the movable element are moved while the surfaces of the stator and the movable element are bonded to each other, leading to larger friction resistance between the stator and the movable element.
Hence, a conventional electrostatic actuator has a rough surface that is formed by fixing conductive beads with an insulating binder on the top surface of a stator, and a smooth surface on the back side of a movable element opposed to the rough surface (for example, JP09-121562).
However, printing or coating of ink (paint) containing beads is likely to cause clogging and a liquid containing beads is likely to coagulate, increasing the occurrence of irregularities on the rough surface.
In the case of a small amount of beads, convex portions are widely spaced with distortion on a film, increasing a flat contact area between the rough surface and the smooth surface. In the case of a large amount of beads, curling is likely to occur with more convex portions in contact with the smooth surface, leading to larger friction resistance.
In the case where the thickness of the insulating binder (resin layer) for fixing beads is smaller than a predetermined value, beads are likely to drop off, whereas in the case where the thickness of the insulating binder is larger than the predetermined value, beads are covered with the insulating binder, precluding the formation of predetermined concave and convex portions on the rough surface.
In other words, in the conventional electrostatic actuator, the concave and convex portions have low uniformity in the plane of the rough surface using conductive beads, unfortunately leading to a local increase in friction resistance between the stator and the movable element.